The present invention relates to a scanning electron microscope for measuring micropattern dimensions, and more particularly to a scanning electron microscope system having a function to control, or correct, a disparity in dimension measurements between measuring scanning electron microscopes, as well as controlling, or correcting, a variation in dimension measurements obtained by a microscope over time. (Such a disparity or variation may be hereinafter referred to as a “tool-to-tool disparity”). The present invention also relates to a tool-to-tool machine control system including scanning electron microscopes and a tool-to-tool matching control apparatus for scanning electron microscopes having such a function.
As semiconductor device patterns have been scaled down in semiconductor manufacturing processes, there has been a need for a dimension measuring apparatus having higher measurement accuracy. The demands related to measurement accuracy include increasing the measurement accuracy of individual measuring apparatuses, reducing disparities in dimension measurements between a plurality of measuring apparatuses provided in a production line, and reducing variations in dimension measurements obtained by a measuring apparatus over time.
Scanning electron microscopes (SEMs) for measuring micropattern width, referred to as “length measuring SEMs” or “critical dimension SEMs” (or “CDSEMs”), have been used to measure the width of micropatterns on the order of a few tens of nanometers. These scanning electron microscopes are capable of capturing a micropattern image at a magnification of a few tens of thousands of times to three hundred thousand times.
Attempts have been made to correct or reduce tool-to-tool disparities in dimension measurements between such measuring scanning electron microscopes or correct or reduce variations in dimension measurements obtained by such a scanning electron microscope over time by correcting the measured values themselves, instead of calibrating the microscopes.
Specifically, Japanese Laid-Open Patent Publication No. 5-248843 (1993) discloses a scanning electron microscope that performs the following steps: for each test sample under each test measurement condition (at each different magnification), finding a correction equation y=a*x+b based on the design value and length measurements; saving these found correction equations from the terminal unit to a disk storage device; and when an actual sample is measured under a given measurement condition, retrieving the correction equation matching this sample and measurement condition, and correcting length measurements using the selected correction equation.